Partial alignment between jets and megamasers: coherent or selective accretion?

Spins play a crucial role in the appearance, evolution and occupation fraction of massive black holes. To date observational estimates of massive black hole spins are scarce, and the assumptions commonly made in such estimates have been recently questioned. Similarly, theoretical models for massive black hole spin evolution, while reproducing the few observational constraints, are based on possibly oversimplified assumptions. New independent constraints on massive black hole spins are therefore of primary importance. We present a rigorous statistical analysis of the relative orientation of radio jets and mega-maser discs in ten low-redshift galaxies. We find a strong preference for (partial) alignment between jets and mega-masers, that can be attributed to two different causes: "coherent" and "selective" accretion. In the first case the partial alignment is due to an anisotropy in the gas reservoir fueling the growth of MBHs. In the second case the spin-dependent anisotropic feedback allows for long-lived accretion only if the orbits of the gas inflows are almost aligned to the MBH equatorial plane. A discussion of the implications of the two accretion scenarios on the evolution of MBHs is presented, together with an outlook on future observational tests aiming at discriminating between the two scenarios and at checking if any of the two apply to different redshifts and black hole mass regimes.